1. Technical Field
This invention relates to a method of decaffeination which comprises contacting a caffeine-containing extract solution with caffeic acid in the presence of water wherein the caffeine and caffeic acid form an insoluble complex and then separating the caffeine/caffeic acid complex from the caffeine extract solution. The caffeine containing extract solution includes any solvent solution, aqueous or nonaqueous, which directly contacts green or roasted coffee for purposes of decaffeination and any subsequent solvent solution, aqueous or nonaqueous, which contacts solvent solutions that have been employed for decaffeination.
2. Background Art
Numerous decaffeination techniques abound in the art. One widely used method is the so-called water decaffeination technique disclosed in U.S. Pat. No. 2,309,092 to Berry et al. In the water decaffeination method, hydrated green coffee beans are extracted with a caffeine-deficient green coffee extract in a multi-stage countercurrent extraction battery. As the green coffee extract progresses through the battery, it becomes increasingly rich in caffeine while contacting decreasingly decaffeinated coffee beans. The caffeine-laden coffee extract withdrawn from the last stage of the battery is treated to remove the caffeine therefrom and subsequently returned to the system. The caffeine is removed from the green coffee extract by contact with an organic solvent, typically a halogenated organic solvent, such as methylene chloride. While the water decaffeination technique enjoys wide application, it is becoming increasingly desirable to avoid the use of organic solvents in food processing.
Additional decaffeination techniques exist, but not without drawbacks. For example, the use of a sugar-loaded activated carbon adsorbent is disclosed in European Patent No. 0,008,398 granted May 19, 1982. While the use of an organic solvent is avoided, the activated carbon adsorbent tends to adsorb non-caffeine coffee solubles as well as the caffeine, severely impairing the economy of the method.
A complexation approach, only with respect to the decaffeination of an aqueous tea extract, is disclosed in U.S. Pat. No. 4,315,036 to Husiani et al. An aqueous tea extract is cooled to precipitate out the cold-water-insoluble complex of caffeine and tannins that are already present in the tea. The method has the advantage of using a complexing compound that is already present in tea and does not then have to be added. Although the tannin/caffeine complex may well be insoluble and therefore precipitate out, such tannins are not present in aqueous coffee extracts.
Many compounds, some native to coffee, are known to complex with caffeine. For example, I. Horman and R. Viani, in "The Nature and Conformation of the Caffeine-Chlorogenate Complex of Coffee" J. Food Sci. 37 (1972) 925-27, recognize ten such caffeine complexes, including the well-studied, water soluble chlorogenic acid/caffeine complex. While it had earlier been speculated that the complexing compounds might be useful in a decaffeination method if it formed a water-insoluble caffeine complex, no such compound native to coffee has heretofore been identified. Moreover, any such native complexing compound would have to compete with the chlorogenic acid and/or break the relatively strong chlorogenic acid/caffeine complex.